Microkeratome blade

ABSTRACT

A microkeratome blade for use for the removal of the epithelial layer and underlying Basement Membrane while leaving a smooth and undisturbed Bowman&#39;s Membrane in preparation for a laser refractive surgical procedure. The blade is capable of cutting through the epithelial layer and Basement Membrane, but not capable of cutting through Bowman&#39;s Membrane.

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/114,808, filed Apr. 3, 2002, currently co-pending.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of refractive surgery and,more particularly, to microkeratomes used for performing laserrefractive surgery.

The human eye in its simplest terms functions to provide vision bytransmitting light through a clear outer portion called the cornea, andfocusing the image by way of a crystalline lens onto a retina. Thequality of the focused image depends on many factors including the sizeand shape of the eye, and the transparency of the cornea and the lens.

The optical power of the eye is determined by the optical power of thecornea and the crystalline lens. In the normal, healthy eye, sharpimages are formed on the retina (emmetropia). In many eyes, images areeither formed in front of the retina because the eye is abnormally long(axial myopia), or formed in back of the retina because the eye isabnormally short (axial hyperopia). The cornea also may be asymmetric ortoric, resulting in an uncompensated cylindrical refractive errorreferred to as corneal astigmatism. In addition, due to age-relatedreduction in lens accommodation, the eye may become presbyopic resultingin the need for a bifocal or multifocal correction device.

In the past, axial myopia, axial hyperopia and corneal astigmatismgenerally have been corrected by spectacles or contact lenses, but thereare several refractive surgical procedures that have been investigatedand used since 1949. Jose Barraquer, M.D. investigated a procedurecalled keratomileusis that reshaped the cornea using a microkeratome anda cryolathe. This procedure was never widely accepted by surgeons.Another procedure that has gained widespread acceptance is radial and/ortransverse incisional keratotomy (RK or AK, respectively). In the 1990s,the use of photoablative lasers to reshape the surface of the cornea(photorefractive keratectomy or PRK) or for mid-stromal photoablation(Laser-Assisted In Situ Keratomileusis or LASIK) have been approved byregulatory authorities in the U.S. and other countries. Recently, a newversion of PRK called Laser Epithelial Keratomileusis (LASEK) has beendeveloped wherein the epithelial layer is soaked in alcohol so as torelease it from Bowman's Membrane and the epithelial layer isnon-destructively rolled aside and the underlying stromal tissue isablated in a manner similar to PRK. This procedure does not always allowfor the smooth removal of the epithelial layer in a single sheet. Inaddition, alcohol is toxic to corneal tissue.

Accordingly, a need continues to exist for a device and method for thesafe, consistent removal of the epithelial layer and Basement Membraneduring a laser refractive surgical procedure.

BRIEF SUMMARY OF THE INVENTION

The present invention improves upon the prior art by providing amicrokeratome blade for use for the removal of the epithelial layer andunderlying Basement Membrane while leaving a smooth and undisturbedBowman's Membrane in preparation for a laser refractive surgicalprocedure. The blade is capable of cutting through the epithelial layerand Basement Membrane, but not capable of cutting through Bowman'sMembrane.

Accordingly, one objective of the present invention is to provide a safeand non-toxic method for the removal of the epithelial layer andunderlying Basement Membrane in preparation for a laser refractivesurgical procedure.

Another objective of the present invention is to provide a method forthe removal of the epithelial layer in preparation for a laserrefractive surgical procedure without the use of toxic chemicals.

Another objective of the present invention is to provide a device thatprovides the safe and non-toxic method for the removal of the epitheliallayer and underlying Basement Membrane in preparation for a laserrefractive surgical procedure.

Another objective of the present invention is to provide a microkeratomeblade that provides the safe and non-toxic method for the removal of theepithelial layer and underlying Basement Membrane in preparation for alaser refractive surgical procedure.

These and other advantages and objectives of the present invention willbecome apparent from the detailed description and claims that follow.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a microkeratome that may be usedwith the invention of the present method.

FIG. 2 is an enlarged partial side view of the microkeratome blade ofthe present invention.

FIG. 3 is a partial cross-sectional view of a human cornea.

DETAILED DESCRIPTION OF THE INVENTION

As best seen in FIG. 1, one microkeratome 34 that may be used with themethod of the present invention generally includes suction ring 10 sizedand shaped so as to affix to eye 12. Ring 10 includes guides 14/16opposite eye 12 that guide cutting head 40 across ring 10. Ring 10 isconnected through translation member 26 to stepper motor 28 forproviding linear movement of cutting head 40 across ring 10. Cuttinghead 40 contains blade 38 that is eccentrically connected to motor 36contained within housing 42 of microkeratome 34. Microkeratome 34 iswell known in the art (see for example U.S. Pat. No. 6,071,293(Krumeich), the entire contents of which being incorporated herein byreference), and commercially available from sources such as AlconLaboratories, Inc., Fort Worth, Tex.

As best seen in FIG. 2, blade 38 generally includes relatively flat side100, tapered side 110 containing rounded section 112 and blunt cuttingedge 114 connecting flat side 100 and rounded section 112. Roundedsection 112 generally has a radius of between about 0.025 millimetersand 0.200 millimeters and is rounded through of angle δ of betweenapproximately 5 degrees and 60 degrees. Blunt cutting edge 114 generallyhas a height H of between approximately 0.001 millimeters and 0.050millimeters, with between about 0.005 millimeters and 0.025 millimetersbeing preferred, and is ground at an offset angle Θ relative to roundedportion 112 at between approximately between 0 degrees and 60 degrees,with between approximately between 0 degrees and 20 degrees beingpreferred. Preferably, rounded section 112 and blunt tip 114 have atextured surface finish. Blade 38 may be made of any suitable material,such as 400 Series stainless steel and may be made using conventionalsurgical blade manufacturing techniques well known in the art.

As best seen in FIG. 3, human cornea 200 has several layers. Theoutermost layer is epithelium 210, followed by Basement Membrane 220,Bowman's Membrane 230, substantia propria or stroma 240, Descemet'sMembrane 250 and endothelium 260. The method of the present inventioninvolves the use of microkeratome 34 having blade 38 to removeepithelium 210 and Basement Membrane 220 while leaving Bowman's Membrane230 relatively intact. The method of the present invention usesmicrokeratome 34 in a conventional manner well known to those skilled inthe art. Preferably, the intraocular pressure of the eye undergoing thesurgical procedure is briefly raised to around 80 mm Hg or greater. Theoscillation frequency of blade 38 preferably is approximately between5,000 revolutions/minute and 20,000 revolutions/minute, withapproximately between 8,000 revolutions/minute and 14,000revolutions/minute being most preferred. The speed of blade 38 as ittraverses cornea 200 preferably is approximately between 1.0millimeter/second and 2.0 millimeters/second, with approximately 1.5millimeters/second being most preferred. As blade 38 approaches cornea200, blunt cutting edge 114 penetrates epithelium 210 and BasementMembrane 220, but is insufficiently sharp to penetrate Bowman's Membrane230. As a result, blunt cutting edge 114 and rounded portion 112 scrapealong the surface of Bowman's Membrane 230, separating epithelium 210and Basement Membrane 220 from Bowman's Membrane 230 without damagingBowman's Membrane 230. Following such separation, Bowman's Membrane 230and stroma 240 are irradiated as in a conventional laser refractivesurgical procedure, see for example, U.S. Pat. No. 4,784,135 (Blum, etal.) and U.S. Pat. No. 4,903,695 C1 (Warner, et al.), the entirecontents of which being incorporated herein by reference.

This description is given for purposes of illustration and explanation.It will be apparent to those skilled in the relevant art that changesand modifications may be made to the invention described above withoutdeparting from its scope or spirit.

We claim:
 1. A microkeratome blade, comprising: a flat lower surface; anupper surface that tapers toward the lower surface, the upper surfacehaving a rounded portion; the rounded portion having a textured surfacefinish; and a blunt cutting edge comprising a substantially flatsurface, wherein the blunt cutting edge is disposed between the lowersurface and the rounded portion of the upper surface, the blunt cuttingedge having a textured surface finish.
 2. The microkeratome blade ofclaim 1 wherein the rounded portion has a radius of between about 0.025millimeters and 0.200 millimeters.
 3. The microkeratome blade of claim 1wherein the blunt cutting edge has a height of between approximately0.001 millimeters and 0.050 millimeters.
 4. The microkeratome blade ofclaim 3 wherein the blunt cutting edge has a height of betweenapproximately 0.005 millimeters and 0.025 millimeters.
 5. Themicrokeratome blade of claim 1 wherein the blunt cutting edge is groundat an offset angle relative to the rounded portion at betweenapproximately between 0 degrees and
 60. 6. The microkeratome blade ofclaim 5 wherein the blunt cutting edge is ground at an offset anglerelative to rounded portion of approximately between 0 degrees and 20degrees.